1. Field of the Invention
This invention relates to a fork lift truck operated by an internal combustion engine and having a carriage which is mounted for movement along the vertically disposed mast or boom carried at the front of the fork lift truck and wherein the carriage is equipped with fork or fork tines that are adapted and arranged to be extended under a load, generally supported by a pallet, which is to be transported from one point to another.
2. Description of the Prior Art
In connection with a fork lift truck driven by an internal combustion engine, it is well known in the art that a hydraulic pump driven by the engine is arranged to supply pressurized hydraulic fluid into a power steering system for decreasing the turning effort of an operator during steering operation of the fork lift, and hydraulic cylinders for lifting the carriage of the fork lift and for tilting a vertically disposed tiltable mast of the fork lift along which the carriage is movably mounted. The fork lift truck of this type has encountered the following problems: during idling of the fork lift truck engine, the engine speed is relatively low and accordingly the amount of the hydraulic fluid discharged from the engine driven pump is decreased below a desirable level, causing a shortage of hydraulic fluid in the hydraulic cylinders for operating the carriage. This shortage of the hydraulic fluid results in lowering the operational speed of the carriage and the tiltable vertical mast along which the carriage is movably disposed.
Furthermore, the hydraulic system of the fork lift truck is arranged such that the power steering system can be preferentially supplied with the hydraulic fluid in order to always obtain secure steering operation. With this connection, the hydraulic fluid always flows through the power steering system. This brings about a further shortage of the hydraulic fluid for actuating the carriage and the tiltable vertical mast, causing the further lowering of the operational speed of the carriage and the tiltable vertical mast.
The thus induced lowering of the operational speed invites inefficiencies in loading and transporting loads. Therefore, in order to obtain the necessary operational speed of the the carriage during the idling condition of the engine, the operator is required to increase the engine speed by operating the accelerator. This accelerator operation troubles the operator, increasing his fatigue.